The efforts to improve electroplating systems and processes have focused on a variety of concerns. One concern is increased output without sacrificing efficiency and, possibly, increased system efficiency. Another concern is improved uniformity of plating thickness and composition across an individual wafer, from wafer to wafer, and from one electroplating compartment to another. Still another concern is the minimization, if not the elimination, of the potential problems associated with human participation in the electroplating process.
For example, human participation in the electroplating process (e.g., assembling/disassembling the electrodes and paddles after each plating cycle or manually immersing/lifting the group of components with the wafer into/out of a cell) can lead to numerous variations. These variations, particularly speed variations in immersion/removal and immersion-to-start-of-plating dwell time, contribute to non-uniformities in deposit thickness and composition.
Existing systems which have attempted to deal with the above concerns include U.S. Pat. No. 3,652,442 (Powers et al.) which discloses an electroplating cell having a single compartment, discrete anode/cathode/paddle components and a rotary-to-linear motion conversion device as the drive means for its paddle. Some drawbacks of the '442 patent include: First, the '442 patent is capable of electroplating only one wafer at a time. Second, while the cathode holder extends from wall to wall, there is no current deflector to adjust the current variation across the wafer--both the wafer and the cathode holder are powered by one power supply. And, third, discrete components typically require setup, positioning and connecting for each plating cycle which can lead to misalignment, mechanical interference, and open circuits.
An IBM Technical Disclosure Bulletin (TDB), Vol. 23, 201 (1980) by L. Berger, R. Bockel, R. Kronemann and D. Meyer describes an improvement over the '442 patent. The TDB discloses the use of current deflectors and shows how to electroplate multiple wafers at a time in one compartment. However, this system uses four current deflectors for each wafer; therefore, to plate six 47 mm-by-47 mm wafers, it is necessary to use 30 separate power supplies to plate 6 small wafers per compartment (6 power supplies for the six wafers and an additional 4 per wafer for the current deflectors). Experiments reveal that it takes more than a week of empirical testing to determine the correct current to be applied to each deflector and each wafer to minimize the compositional and thickness variations. Despite these time-consuming efforts, the resulting non-uniformities remain large.
U.S. Pat. No. 4,102,756 (Castellani et al.) discloses a method and apparatus for electroplating. The '756 patent focuses on composition and the operation of the permalloy plating bath, pH and iron measurements and adjustments, bath filtration and the locations where the plating solution enters and exits the plating cell. The '756 patent shows, in FIG. 2, the concept of using many wafers per cathode holder but does not describe the use of current deflectors and does not use a separate symmetrical compartment and separate paddle for each wafer.
U.S. Pat. No. 5,078,852 (Yee et al.) discloses a plating rack with a ring-shaped thieving electrode coplanar with the workpiece surface. However, the '852 patent does not disclose a configuration with insulating side walls forming a symmetric compartment. In addition, the '852 patent does not disclose a symmetrically opposing anode, a thieving electrode which occupies all of the rack surface not occupied by the workpiece, individual currents fed to the workpiece and the thief, or an agitation paddle.